X-ray tube kilovoltage control system

ABSTRACT

A system for automatically supplying a preselected kilovoltage to an X-ray tube is provided with a transformer having a plurality of binary-coded secondary windings. Switching devices are connected to the secondary windings to provide various combinations of secondary windings. A control system automatically changes the combination of secondary windings to correct for changes in system parameters to insure that a selected kilovoltage is actually applied to the X-ray tube at the start of an exposure.

United States Patent Inventor Walter E. Splain Solon, Ohio Appl. No.743,421

Filed July 9, 1968 Patented Dec. 28, 1971 Assignee Picker CorporationWhite Plains, N.Y.

X-RAY TUBE KILOVOLTAGE CONTROL SYSTEM 30 Claims, 5 Drawing Figs.

U.S.Cl 250/103, 315/276, 323/435 Int. Cl H05g 1/32, G03b 41/16 FieldolSearch 250 102,

[56] References Cited UNITED STATES PATENTS 2,840,718 6/l958 Wright eta1. 250/103 X 3,255,403 6/1966 Beaver et al. 323/435 PrimaryExaminer-James W. Lawrence Assistant Examiner-A. L. BirchAttorney-Watts, Hoffmann, Fisher & i-ieinke ABSTRACT: A system forautomatically supplying a preselected kilovoltage to an X-ray tube isprovided with a transformer having a plurality of binary-coded secondarywindings. Switching devices are connected to the secondary windings toprovide various combinations of secondary windings. A control systemautomatically changes the combination of secondary windings to correctfor changes in system parameters to insure that a selected kilovoltageis actually applied to the X-ray tube at the start of an exposure.

PATENTED 0:328 IBTI SHEET 5 OF 5 IN VENTOR.

WQLTE? E. SPLA/N M A TOQNEm X-RAY TUBE KILOVOLTAGE CONTROL SYSTEMBACKGROUND OF THE INVENTION 1. Field of the Invention.

The present invention relates generally to X-ray systems, and moreparticularly, to a control system for selecting kilovoltages to besupplied to an X-ray tube, while taking into account various losses andfluctuations to insure that a selected kilovoltage is actually appliedto the tube at the start of an exposure.

2. Description of the Prior Art. n

In X-ray apparatuses the kilovoltage (KV) supplied to an X- ray tube isadjustable so that different intensities of X-rays can be provided, andso that the system can be used for different X-ray procedures, such asfluoroscopy and radiography. The demands for flexibility and reliabilityof KV are continually increasing as new procedures are developed, anddevices such as image intensification tubes with television and/or cinecameras are more frequently used.

In prior X-ray systems, adjustment of the KV was often provided by anautotransformer between the power supply and the usual high-tensiontransformer connected to the X-ray tube. These prior systems are quitecomplex generally and are not sufficiently flexible and reliable for themay uses demanded of present day X-ray systems. For example, an X-raysystem should be usable for at least fluoroscopy, radiography, andcinematography.

The power requirements for fluoroscopy are quite different from thosenecessary for radiography and for cinematography. During the examinationof a patient, these procedures are often alternately and sequentiallyused. For this reason, it is necessary for the X-ray system to be easilyand substantially instantaneously adjustable from one use to another.

A typical prior system, which attempted to provide this flexibility, hadtwo variable-tap autotransformers or the equivalent. One autotransformerwas set usually for its secondary winding to meet the requirements ofradiography, and the other was set to a compromise setting which soughtto satisfy the requirements of both fluoroscopy and cinematography. Themedical practitioner in examining a patient switched the primaryterminals of an X-ray tube high-voltage transformer from the secondaryterminals of one autotrans former to those of the otherautotransforrner, when changing between fluoroscopy or cinematographyand radiography studies. In order to perform this switching function,complex switching mechanisms are necessary between the autotransformersand the high-voltage transformer. The switching problem is complicatedby the use of only one KV level for both cinematography and fluoroscopy,even though the power levels are different.

With the prior systems, automatic adjustment of the KV applied to theX-ray tube for a given study was not provided. It has generally beennecessary to adjust the autotransformer secondary winding settingsmanually in order to change the applied KV. In radiography, precisepower levels must be used to obtain proper exposure. Accordingly, akilovoltage meter has been provided in prior X-ray systems forindicating voltage measurements during radiographic procedures. Thus,another shortcoming of the prior art has been the need to observe the KVmeter and manually adjust the KV for a desired level.

In the past, a kilovoltage meter has not usually been used for providingvoltage measurements during fluoroscopy procedures, because thestability requirements have not been as great as in radiography and themeter was not of appropriate voltage range for fluoroscopy. Because nokilovoltage meter was used during fluorosc py, the operator was notaware of changes that might have taken place in desired kilovoltagecaused, for example, by line voltage changes. Thus, such prior systemswere not generally capable of accurately providing desired power levelswhen line voltage changes occurred prior to fluoroscopic examinations.

SUMMARY OF THE INVENTION The present system provides for automaticcontrol of the voltage applied to an X-ray tube at the start of anexposure, regardless of whether the X-ray system is being utilized forfluoroscopy, radiography, cinematography or any other procedure. Thepresent system does not require even one kilovoltage meter, because anychange in the voltage supplied to the X-ray tube is correctedautomatically prior to the exposure being made. The present systemcorrects for direct current voltage losses caused by the resistance ofthe secondary windings of the high-tension transformer. It alsocompensates for voltage losses which occur across the rectifier tubes inthe secondary of this high-tension transformer. It further compensatesfor supply line voltage changes. Finally, it compensates for currentchanges caused by a change in applied line voltage by making apercentage voltage change.

The present system also provides for rapid and automatic changes in thekilovoltage selected to be applied to the X-ray tube. In addition,changes in voltage settings required to switch from fluoroscopy toradiography or to cinematography are automatically and rapidly providedwith one autotransformer. The present system is particularly adapted foruse in a preprogrammed system, wherein several kilovoltage settings forseveral different studies using radiography, fluoroscOPY orcinematography are preset prior to the beginning of an examinationprocedure and are automatically changed from one to another when runningthe several different studies.

In the present system, an autotransforrner is provided having aplurality of secondary windings, all wound differently to providedifferent secondary voltages. The secondary windings are binary coded ina series, in that each winding provides twice the secondary voltage of aprevious winding, so that the secondary windings provide voltages whichby a common factor are the elements of the binary geometric series, 1,2, 4, 8, l6, etc. Thus, a second winding provides twice the voltage of afirst winding and a third winding provides twice the voltage of thesecond winding, and so forth, each succeeding winding providing twicethe secondary voltage of a next preceding winding.

Suitable switching devices are provided to interconnect these secondarywindings. The switching devices selectively connect the secondarywindings in various combinations to provide virtually any desired outputvoltage from the autotransformer secondary. The output voltage can bevaried from a minimum voltage which is the voltage across a secondaryreference winding, to the voltage across the combination of all of thesecondary windings, the latter being a maximum voltage setting. Theparticular combination of secondary windings necessary to provide aselected voltage is provided automatically in response to the setting ofa particular kilovoltage level by an X-ray control system. This controlsystem also changes the selected combination of secondary windings toautomatically correct the kilovoltage to be applied, prior to the startof an exposure, for changes that occur in supply line voltage, losses inthe secondary circuit of the high-voltage transformer, current changesdue to a change in the applied line voltage, and other losses.

Other advantages, features and objects of the invention and a fullerunderstanding of it, may be had by referring to the followingdescription and claims taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a partially block andpartially schematic diagram of an autotransformer and its voltageselector relays in an X- ray system embodying the invention;

FIG. 2 is a block diagram of a relay control for controlling the voltageselector relays shown in FIG. 1;

FIG. 3 is a schematic diagram of a relay driver used in the relaycontrol of FIG. 2; FIG. 4 is a schematic diagram of an accumulator usedin the relay control of FIG. 2; and

FIG. 5 is a schematic diagram of various other circuits shown as blocksin the relay control of FIG. 2.

As shown in FIG. 1, an X-ray system embodying the invention includes apair of input terminals 14, 12 which are connected to a suitableconventional alternating current voltage source (not shown). The inputterminals 111, 12 are respectively connected to a primary winding 141 ofan autotransformer 14 through ganged, normally open contacts 16A, 16B ofan input power switch, indicated generally by the numeral 16. Thetransformer primary winding 141 is provided with a plurality of inputterminals 14P1-14P10 to accommodate input line voltages of variouslevels. In practice, the switch 16 would probably be a power relay whoseactuation is controlled by an ON-OFF control.

The autotransformer 14 includes a plurality of secondary windings 1481,1482, 1484, 1488, 14816, 14832, 14864, 148A, 1488, 148C, 148R, thewindings 14832, 14864, 148R being defined by taps on the primary winding141. The secondary windings 1481-14864 are wound to provide differentrespective output voltages. The output voltage appearing across theterminals of one of the secondary windings 1481-14864 is twice theoutput voltage appearing across the output terminals of the immediatelypreceding secondary winding taken in numerical order, as indicated bytheir reference numerals. In other words, the voltage appearing acrossthe terminals of the winding 1482 is twice that appearing across thewinding 1481. The voltage across the winding 1484 is twice that acrossthe winding 1482, and so forth, such that the voltages across thewindings 1481-14864 are equal, by a common factor, to the elements of abinary, geometric series, i.e., 1,2,4,8,l6,32,64. 1f the voltage acrossthe first winding 1481 is arbitrarily designated as having a value of 1,then the voltage across the winding 1482 has a value of 2, the voltageacross the winding 1484 has a value of 4, the voltage across the winding1488 has a value of 8, the voltage across the winding 14816 has a valueof 16, the voltage across the winding 14832 has a value of 32, and thevoltage across the winding 14864 has a value of 64. A particular voltageis provided by adding the output voltages of selected ones of thewindings 1481-14864 to a base or reference voltage provided from thewinding 148R, so that the total output indicates the particular selectedvoltage. If a common voltage factor of the arbitrary values 1, 2, 4,etc. is 1.0 volts, then a voltage range of 1-127 volts can be selectedform the secondary windings 1481-14864 and added to the referencevoltage from the winding 148R of, for example, 20 volts. In the systemshown, a common voltage factor of 1.0 kv. is preferably used torepresent the voltage ultimately supplied to an X-ray tube. Thus, thatvoltage may be varied from a base or reference level of 20 kv. up to 147kv. in single-kv. steps.

The secondary windings 148A, 148B, 148C are exemplary of a plurality ofauxiliary windings for energizing power supplies, etc. One of them, forexample the winding 148A, is pro vided with a pair of terminals 18A,1813, that are connected to a reference voltage power supply to be laterdescribed in connection with F168. 2 and 5.

A plurality of relays 20, 22, 24, 26, 28, 311, are provided forconnecting together in series various ones of the secondary windings1481, 1482, 1484, 14811, 14816, 14832, 14864, 148R to provide a selectedoutput voltage. Each of the relays 26-32 is provided with two sets ofnormally open contacts, one set of normally closed contacts, and anactuating coil. in the case of the relay 20, the normally open contactsare designated as 211A and 20D, the normally closed set of contacts isdesignated as 21113, and the actuating coil is designated as 20C.Similar contacts and coils of the other relays 22-32 are similarlydesignated. Each of the relay coils 2(1C-32C has one end connected to alead 34, which is in turn connected to ground through a normally openset of relay contacts 36A. The other ends of the relay coils 20C32C arerespectively connected by means of leads 38-50 to a relay driver shownin FIGS. 2 and 5.

Output from the selected combination of secondary windings of thetransformer 14 is provided on a pair of condoctors 52, 54. The conductor52 is connected directly to one input terminal of a conventionalhigh-voltage transformer and rectifier circuit 56. The conductor 54 isconnected to another input terminal of the high-voltage transformer andrectifier circuit 56 through a silicon controlled rectifier switch 58.The silicon controlled rectifier (SCR) switch 58 is entirelyconventional in design and is controlled in conventional manner by asignal applied to an input lead 60. The derivation of the control signalapplied to the lead 61) will be later described in conjunction with FIG.2. Two output terminals of the high-voltage transformer and rectifiercircuit 56 are connected respectively to the anode and cathode of aconventional X-ray tube 62 to provide high-voltage to the tube.

Looking now at the specific connections of the transformer secondarywindings and the relays, it is seen that the contacts 2110-321) serve asholding contacts for their respective relays. Even more specifically,each of the contacts 20D-32D is connected to a lead 64, which is in turnconnected to a source of positive potential (not shown). Each of thecontacts 20D-32D is connected to that end of its corresponding relayactuating coil ZOE-32C that is remote from the lead 34. Thus, once oneof the relay coils 211C-32C is energized by a signal being applied toits corresponding lead 38-51), the corresponding contacts 260-321) closeto maintain the corresponding relay coil energized so long as the relaysection 36A is closed to provide a current path to ground.

The output line 52 is connected to the contact 2081 of the relay 20, andthe output line 54 is connected to both of the contacts 32A2 and 32132of the relay 32. The conditions of the A and B contacts of the relays211-32 determine which of the secondary windings 1481-14864 areconnected between the output lines 52-54. The relay contact 20B2 isconnected directly to the contact 2281, and the contact 2282 isconnected to the contact 2451, the contact 24132 is connected to thecontact 2681, the contact 2682 is connected to the contact 21181, andthe contact 28132 is connected to the contact 31181. It is particularlypointed out that the contact 30B2 is not connected directly to thecontact 3231, but rather is connected to that contact through thesecondary winding 148R. Thus, even if all the relays 20-32 aredeenergized and all the B contacts are closed, the secondary winding148R will still be connected between the output leads 52-54. It will berecalled that this is the secondary winding that provides a base orreference voltage to which the voltages from selected other ones of thesecondary windings are added.

Various ones of the transformer secondary coils 1481-1486 4 areconnected in series with the reference voltage secondary 148R by openingselected ones of the B sections of the relays 211-32 and closingcorresponding A sections. As shown, one end of the secondary winding1481 is connected directly to the output lead 52, and the other end ofthat line is connected to the relay contact 20A1l. One end of thesecondary winding 1482 is connected to the contact 20.42 and to thecontact 20132. The other end of that winding is connected to the contact22.41. One end of the secondary winding 1484 is connected to thecontacts 22A2, 22B2, and the other end of that winding is connected tothe contact 24A]. One end of the winding 1481" is connected to thecontacts 24A2, 24B2, and the other end of that winding is connected tothe contact 26A1. One end of the winding 14816 is connected to thecontacts 26A2, 2682, and the other end of that winding is connected tothe contact 28All. The relay contacts 28A2, 28132, 311A1, 31181 are allconnected together. One end of the secondary winding 14832 is connectedto the contact 30A2, and the other end of that winding is connected tothe contact 3082. The secondary winding 14864 is connected between thecontacts 321 11, 32131 and, as previously mentioned, the output lead 54is connected to the contacts 32A2, 3282.

Assume for purpose of illustration that it is desired to add 1 volt tothe voltage produced by the secondary winding 148R. ln that situation, asignal would be provided on the lead 38 to energize the relay 20. Thecontacts D would close to maintain the coil 20C in energized condition,the contacts IZ EB would open, and the contacts 20A would close. If allof the other relays remain deenergized, the current path between theoutput conductors 52, 54 would be through the secondary winding'l4Sl,the contacts 20A, 22B, 24B, 26B, 28B, 30B, the secondary winding 148R,and the relay contacts 328. This assumes, of course, that the relaycontacts 36A are closed so that the relay-actuating coils may beenergized.

Assume now as a second example that it is desired to add 27 volts to thebase or reference voltage provided by the secondary winding 148R. Inthat situation, signals would be received on the leads 38, 40, 44 and46. This would cause the relays 2b, 22, 26 and 28 to change theirconditions. This would connect the output lead 52 to the lead 54 throughthe secondary winding 1481, relay contacts 20A, secondary winding M82,relay contacts 22A, relay contacts 248, secondary winding 1488, relaycontacts 26A, secondary winding 14816, relay contacts 28A, relaycontacts 30B, secondary winding 148R, and relay contacts 328. Thus, itis apparent that various ones of the relays 20-32 may be energized toconnect selected ones of the secondary windings 1451-14864 in seriesbetween the output leads 52-54 to provide selected output voltagesvariable in 1- volt steps over a range of 127 volts, the selected voltsbeing added to those provided by the secondary winding 148R.

FIG. 2 illustrates in block diagram form a relay control for controllingand driving the relays 20-32 shown in FIG. 1. The various elements ofthe system including leads that are common to various figures areidentified by the same reference numerals throughout.

As shown in FIG. 1, the actuating coils 20C-32C of the relays 20-32 arerespectively energized through the leads 38-50. Those leads are shown inFIG. 2 as output leads from a relay driver 70. Basically, the relaydriver 70 serves to connect selected ones of the leads 38-50 to a sourceof positive potential in response to a command signal from a firstmultivibrator 72 on a lead 73. The selection of which one or ones of theleads 38-50 are energized is controlled by an accumulator 74.

The accumulator 74 is, in effect, a binary counter. It counts pulsessupplied to it on a lead 75 from a clock pulse generator 76 through agate 78. When the accumulator is receiving pulses from the pulsegenerator 76, it counts continuously from 127 to 0 and then recycles.For each count, two types of output signals are provided. First, outputsignals are provided on one or more of a plurality of leads 80-92 thatenable the relay driver 70 to provide signals on corresponding ones ofthe leads 38-50 when so commanded by the multivibrator 72. Second,current output signals are provided through one or more of a pluralityof resistors 94-106 connected together in a current adder configuration.The sum of the currents through the resistors 94-106 is supplied as oneinput to a current comparator 108 on a lead 110.

Energizing voltage for the accumulator 74 is provided by a power supply112 on a lead 114. Input to the power supply 112 is from the terminals18A, 1813, which are connected to the secondary winding 148A of theautotransformer 1141 described in connection described in connectionwith FIG. 1. Thus, the voltage output of the power supply 112 to theaccumulator 74 on the lead 114 will reflect any variations in the linevoltage input to the entire system. Consequently, the currents throughthe resistors 94-106 and through the lead 110 will reflect any such linevariations as a percentage variation. Current is also supplied from thelead 1 14 through a lead 116 and a variable resistor 118 to the lead110. The variable resistor 118 provides current to the comparator 103that corresponds to the minimum KV to be applied to the X-ray tube asdetermined by the transformer secondary winding 148R. The variableresistor 118 is referred to as the Low KV Adjust.

The voltage supplied by the power supply 112 is also adjusted inaccordance with three other factors, which cause various voltages to beadded to the output voltage of the power supply.

First, an adjustable voltage is added to the power supply voltage sothat the maximum current output of the accumulator 74 on the lead 1ll0corresponds to the maximum KV that is to be applied to the X-ray tube.This voltage is controlled by the setting of an adjustable arm of apotentiometer 120 connected between a positive direct current source andground. This is known as the High KV Adjust.

Second and third, the potential controlled by the setting of thepotentiometer 120 is modified by potential drops across an adjustableportion of a potentiometer 122 and across an MA adjustment 124. Thevariable arm of the potentiometer 122 is set to compensate for the linevoltage drop occurring between no loa and full load" conditions, and mayrepresent a voltage drop of 2.5 percent-l0 percent in the line voltagewhen the X-ray tube is energized. This would not be compensated for by achange in the AC input (at terminals 18A, 188) to the power supply,because that change would occur when the exposure starts after theautotransformer secondary windings had been selected and could not bechanged.

The MA adjustment 124 may be thought of as a variable resistorconnecting the movable arm of the potentiometer 122 to ground and whoseresistance varies inversely with the selected X-ray tube current.Inasmuch as variation in its value varies the voltage applied to theaccumulator 74, the current output of the accumulator 74 varies as afunction of both KV and X-ray tube current; those variations areproportional to losses that vary as the'product of KV and X-ray tubecurrent (KV MIA). Such losses are primarily those that occur in theautotransformer primary and in the powerline and are dependent on bothRV and MA.

The voltage appearing across the MA adjustment 124 and the selectedportion of the potentiometer 122 is applied to the negative side of thepower supply 112 through an impedancematching device 125 interposed in alead 126. The impedance-matching device 125 draws no current through thepotentiometer 122 and hence isolates the power supply 112 from thepotentiometers I20, 122 and the MA adjustment 124. The voltage added tothe power supply voltage is actually provided from theimpedance-matciing device 125, under control of the potentiometers 120,122 and the MA adjustment 124. In a particular example, about +1 2 voltsDC may be provided by the power supply 112, and about +12 volts DC maybe provided from the impedance-matching device 125. These voltages ofcourse vary in accordance with the factors previously mentioned.

As previously mentioned, current is supplied to one comparison input ofthe comparator 108 through the lead 110. Current is taken from a secondcomparison input of the comparator through a lead 127. Current issupplied through the lead 127 to an MA adjustment 128, and to either oneof a programmed KV (fluoroscopic) control or a programmed KV(radiographic) control 132. Determination of whether the control i319 orthe control 132 receives current through the lead 127 is controlled by asignal applied to them from a mode control switch 134.

The MA adjustment 128 represents a variable impedance, and its value isselected so that current through it is proportional to high-voltagetransformer secondary losses that are directly proportional to the X-raytube current and not to KV. These losses are static for each selectedtube current, and once an X-ray tube current is selected the currentthrough the MA adjustment 128 remains constant for that setting. Thus,the setting of the MA adjustment 128 provides a current drain from thecomparator 108 through the lead 127 proportional to X-ray tube current.

The programmed KV controls 130-132 respectively drain currents from thelead 126 that are proportional to various values of KV to be applied tothe X-ray tube for fluoroscopy and radiology. The fluoroscopic KVcontrol 130 contemplates the drain of a current that is continuouslyadjustable in value over a predetermined range of values under themanual control of a radiologist. The radiographic KV control 132contemplates the drain of a current that is adjustable in steps,

each step corresponding to a change of one KV in the voltage applied tothe X-ray tube. Both the fluoroscopic ICV control ll3tl and theradiographic lKV control 132 will be later described in more detail inconnection with FIG. 5.

The comparator 108 is essentially a current comparator that compares thecurrents through the lead 1110, 127 and, if those currents aresubstantially equal, provides a high output signal. If the currentsthrough those leads are unequal, the comparator provides a low outputsignal. The sensitivity of the comparator ltlh may be adjusted toprovide a desired dead zone, so that minor differences between thecomparison currents will not cause the comparator to provide a lowoutput signal. This is done by adjustment of the resistance of avariable resistor 1136 connected between the lead llllt) and anotherinput to the comparator 1%. Of course, this will be explained in moredetail in connection with the circuit diagram of the comparator shown inFIG. 5.

The output signal from the comparator h appears on a lead 1138, which isconnected to a first control input of the gate 78 interposed between theclock pulse generator 76 and the accumulator 7 3, and to an input of arelay driver M0. A second input of the gate 7% is connected by a lead Mlto receive an output signal from the relay driver Mil. The clock pulsegenerator 7d runs continuously while the equipment is energized.However, its output pulses are only transmitted through the gate 7% tothe accumulator 74 when the signals on the leads 138, Ml are low. Whenthe signal appearing on either of the leads 138, Ml is high, the gate 78is closed and no clock pulses are permitted to reach the accumulator 71.

The gate 7% may be maintained in a closed condition once it has attainedthat condition and regardless of later-occurring output signals from thecomparator 11.08, by grounding an input to the relay driver 140 througha normally open switch M2. This switch when open prevents a high outputsignal from the comparator 108 from actuating the relay driver 140.Thus, when the switch 142 is open, a high output signal from thecomparator Mid can close the gate 78. However, the gate will open if theinput signals to the comparator become unequal for any reason and willremain open until the inputs to the comparator become equal again.

The switch 142 serves as the exposure control or command switch. When itis in its normal, open position, a low or ground level signal issupplied on the lead Ml. to permit the gate 78 to be open or closedunder the control of the accumulator. When the switch M2 is closed, thenext-appearing high signal from the comparator actuates the relay driverto provide a high signal on the lead Ml. This signal will continue andmaintain the gate 78 closed until the switch 1142 is opened at the endof an exposure.

When the switch 142 is first closed, the output signal from thecomparator 1108 applied to the input of the relay driver 114MB and tothe gate 78 may be either high or low. if the current comparison signalsto the comparator 10% on the leads iii], R27 are not equal, the outputof the comparator is low. The low output signal appearing on the lead1133 opens the gate 78 and permits the clock pulses from the clock pulsegenerator 76 to be provided to the accumulator 74. As the accumulatorcounts the clock pulses applied to it, various ones of the leads hilt-92and M-lltld are energized in conventional binary counting fashion.Current through various combinations of the resistors M406 changes thecurrent being provided to the input of the comparator 108 on the leadllltl. When the currents in the leads 110, 127 are equal, the outputsignal of the comparator lllii changes from low to high. This highsignal on the lead Mid causes the gate 78 to close so that no furtherpulses are provided to the accumulator 74 That high signal on the lead138 also actuates the relay driver M0 and a high signal appears on thelead Mil to maintain the gate 7% closed regardless of further signalsfrom the comparator. Thus, the accumulator is in effect frozen" at itslast count. Of course, these effects occur immediately if the comparatoris balanced and is providing a high output signal at the time the switchM2 is first closed. This may well be the case, unless there are changesin the input line voltage occurring at the time the switch M2 is closed.

When the relay driver M0 is actuated, it energizes a relayactuating coil36C. The relay coil 36C controls relay sections 36A, 36B. The relaysection 36A, which is normally open, is shown in FIG. l as connectingthe conductor 34 to ground. It will be recalled that the conductor 34 iscommon to all of the relay actuating coils INC-32C. The relay section363, when the coil 303C is energized, connects an input of themultivibrator 72 to ground, thus energizing that multivibrator.

The multivibrator 72 is essentially a delay element, whose function isto insure that the relay section 36A has completely pulled in before apositive firing pulse is supplied on the lead 73 to the relay driver 7%to energize a selected one or ones of the output leads 385ll. Aspreviously pointed out in connection with FIG. ll, energization of theleads 3850 causes energization of corresponding ones of the relay coils20C32C to provide a selected voltage from the secondary windings14811-14864 of the autotransformer 14 through the SCR switch 58 to theHV transformer and rectifier circuit 56 for the X-ray tube 62. Whenselected ones of the relays 20-32 are energized, their correspondingcontacts 20A-32A and ZtiD-32D are closed. As previously noted, thecontacts 2ilD-32ll) serve as holding contacts, so that once the selectedrelays are momentarily energized the leads 3850 may be deenergized.

it is essential that the selected ones of the relays 20-32 have theircontacts 20A-32A fully closed before power is applied through the SCRswitch 58 to the HV transformer and rectifier circuit 56. To this end, asecond delay multivibrator 144 is provided. It is actuated by a pulsefrom the first multivibrator 72 that occurs simultaneously with therelay driver firing pulse on the lead 73. This multivibrator provides asecond delay after the thing pulse is provided from the multivibrator 72to the relay driver 70 before it provides a positive signal on the leadso to close the SCR switch 58 and apply voltage from the lead 54 to theHV transformer and rectifier circuit 56.

The delay multivibrators 72, 144 are entirely conventional one-shotmultivibrators, and are well known in the art. Hence, they are not shownschematically.

FIG. 3 is a schematic diagram of the relay driver 70 shown in block formin FIG. 2. Fundamentally, the relay driver 70 is composed of sevenindividual driver sections, indicated generally by the referencenumerals l50A-G. The sections A-G are associated with corresponding onesof the relays 20-32 and are connected to them by means of correspondingleads 38-50. inasmuch as the driver sections l50AG are identical to eachother, one general description will be given that is applicable to allsections with corresponding elements in the seven sections beingdesignated by the same reference numerals with sufiixes A-G.

Each of the driver sections ll5tl comprises a silicon controlledrectifier (SCR) 152. The anodes of all of the SCRs l52A-G are connectedtogether and through a common lead 154 to a source of positive DCpotential (not shown). The cathodes of the SCRs are connected throughcorresponding disconnect diodes l56A-G to corresponding ones of theleads Bi -fit), shown also in FIG. l as connected to the actuating coilsZilC-32C of the relays 204%). Current through the lead 1541 from thepositive power supply through selected ones of the SCRs l52A-G and thedisconnect diodes l56A-G is used to energize the relays 20452 initiallybefore their corresponding holding contacts Mill-32D close.

Each of the SCR's l52A-G has a gate electrode, which receives signalsfrom two different sources. Coincidence of the two signals is requiredin order to fire the corresponding SCR. First, each gate electrode isconnected through a resistor 158 to a lead 160. Signals are provided onthe lead 160 from the lead 73 through a capacitor 162. As previouslymentioned in connection with the description of FIG. 2, a positive pulseis provided on the lead 73 from the first multivibrator 72 a short timeafter the relay section 36B closes. The lead 160 is connected to groundthrough a resistor 164, so that the capacitor 162 and the resistor 164act as a ditferentiator to apply a positive spikelike pulse through theresistors 158 to the gate electrodes of the SCRs 152 each time apositive output pulse is provided from the multivibrator 72. Thus, theSCRs 152 are pulsed, rather than continual power being supplied intotheir gate electrodes.

As previously mentioned, signals also can appear on various ones of theleads 80-92 from the accumulator 74 shown in block form in FIG. 2. Whichof these leads bear positive signals depends on the particular count inthe accumulator 74 at any given instant. Those leads 80-92 which do notbear positive signals are effectively grounded through the accumulator74, so that a positive firing pulse appearing on the lead 160 isdissipated to ground and does not fire any of the corresponding SCR's.

The gate electrodes of the SCRs 152A-G are connected to their cathodesthrough resistors l66A-G connected in parallel with capacitors 168A-G.

When one or more of the leads 80-92 have positive signals thereon fromthe accumulator 74 and a positive firing pulse is received on the lead160, those SCRs whose gate electrodes are positive due to signals on theleads 80-92 are fired. This effectively connects the positive voltage onthe lead 154 to the output lead or leads 38-50 of those SCRs that havefired. This energizes a selected one or ones of the relays 20-32 (FIG.1). When a relay 20-32 is energized, its holding contacts close. Thisremoves any current through its corresponding SCR 152, and that SCRextinguishes. Thus, it is seen that the relay driver 70 is onlyoperative during the pull-in times of the relays 20-32.

The diodes 156 serve to prevent any reverse current flow from the relaycoils into the driver 70. The resistor 166 and the capacitor 168 providea finite gate impedance, so that the gate does not appear to be open,which might cause noise to fire the SCRs. They also serve to suppressany leakage current that might be in their corresponding SCR. Theresistors 158 serve to isolate the firing pulse appearing on the lead160 from the accumulator 74, and also act as current dividers for thefiring pulse appearing on the lead 160. Were the resistors 158 not inthe circuit, only one of the he SCRs 152 would fire because its gateelectrode-cathode junction would present a very low impedance.

The accumulator 74, shown schematically in FIG. 4, fundamentallycomprises seven conventional direct-coupled, bistable multivibrators170A-170G. Inasmuch as all of the multivibrators 170 are identical, onlyone description will be given which is applicable to all of them.Corresponding elements in the seven multivibrators are designated by thesame reference numerals with A-G suffixes.

Each multivibrator comprises a pair of NPN-transistors 172, 174, and isprovided with an NPN-transistor 176 that serves as an output or clampingtransistor. The emitters of the transistors l76A-G are connecteddirectly to ground, and their collectors are respectively connected tothe leads 80-92 that connect the accumulator 74 to the relay driver 70.Thus, when one of the transistors l76A-176G is conducting, acorresponding one of the leads 80-92 is effectively connected to groundto prevent a firing pulse on the lead 160 (F16. 3) from firing any oneof the SCRs 152. When the transistors 176 are nonconducting, the gateelectrodes of the corresponding transistors 152 in the relay driver 70are enabled to respond to a positive firing pulse on the lead 160provided from the multivibrator 72.

Referring momentarily to FIG. 2, it is seen that the clock pulses fromthe clock pulse generator 76 are provided through the gate 78 on a lead75 to the accumulator 74. As seen in FIG. 4, the lead 75 is connected toone side of a capacitor 178, whose other side is connected to groundthrough a resistor 180. The capacitor 178 and the resistor 180 serve todifferentiate the relatively square clock pulses received on the lead 75and provide relatively sharp negative pulses to the accumulator 74. Adiode 181 provides a discharge path for the capacitor 178.

In each section 170A-170G of the accumulator 74, the negative-goinginput pulse is provided to the cathodes of a pair of steering diodes182, 183. The negative-going input pulse is coupled from the anode ofthe diode 182 through a resistor 184 and capacitor 186 connected inparallel to the base of the transistor 172. it is also coupled from theanode of the diode 183 through a resistor 188 and capacitor 190connected in parallel to the base of the transistor 174. The base of thetransistor 172 is also connected through a resistor 192 and a lead 193to a source of negative DC potential (not shown). The anode of the diode182 is also connected to the next stage in the accumulator through acapacitor 194. The emitters of the two transistors 172, 174 in eachstage are connected together and directly connected to ground. Thecollector of the transistor 172 is connected to the lead 114 from thepower supply 112 through a load resistor 196. The collectors of thetransistors l72A-172G are also connected to an end of the correspondingoutput resistor 94-106. The collector of the transistor 172 is alsoconnected through the parallel combination of the resistor 188 and thecapacitor 190 to the base of the transistor 174 in that stage. The baseof the transistor 174 is connected to the negative potential lead 193through a resistor 198. The collector of the transistor 174 is connectedto the positive lead 114 from the power supply 112 through a loadresistor 200, and is also connected to the side of the couplingcapacitor 194 remote from the next-succeeding stage. The collector ofthe transistor 174 is also connected through a resistor 202 to the baseof the transistor 176 that was previously mentioned as being the outputor clamping transistor that controls a corresponding section of therelay driver 70.

it is apparent that for current to flow through any one of the outputresistors 94-106 a corresponding transistor l72A-G must benonconductive. Otherwise, current would flow from the lead 114 throughthe resistor 196, and directly through the transistor 172 to ground. Ifa transistor 172 is nonconductive, current will flow from the lead 114through the resistor 196, and through a corresponding output resistor94-106. The values of the resistors 94-106 are chosen in accordance withthe desired current flow corresponding to the binary code 1, 2, 4, 8,16, 32, 64. In other words, if the resistor 94 is assumed to have avalue of unity, the resistor 96 would have a value of one-half, theresistor 98 a value of one-quarter, the resistor 100 a value ofone-eighth, the resistor 102 a value of one-sixteenth, the resistor 104a value of one thirty-second, and the resistor 106 a value of onesixty-fourth. Therefore, current through the resistor 96 would be twicethat through the resistor 94, and so on progressively throughout thebinary series.

It is pointed out that the accumulator 74 counts backwards. That is, itstarts with a count of I27 and counts down to zero, at which time itrecycles. This is completely immaterial to the operation of the controlsystem of the invention, because at some time during each counting cyclethe output current on the lead to the comparator 108 (FIG. 2) will beequal to the current on the lead 127. At that time, the proper ones ofthe clamping transistors 176 will release the clamps on the leads 80-92and condition the corresponding driver sections A-G to energize thecorresponding relays 20-32 upon receipt of a firing pulse from themultivibrator 72.

As an aid to understanding the operation of the accumulator 74, assumethat at some instant it has reached a zero count, so that the currentoutput on the lead 110 from the accumulator is substantially zero. Ofcourse, there will be an output current on the lead 110 because ofcurrent through the low-KV- adjust resistor 118 which corresponds to thebase or reference applied KV of approximately 20 kv.

At that time when the accumulator 74 registers zero, all of thetransistors 172 are conductive, which maintains the bases of thetransistors 174 at a negative potential and hence the latter transistorsnonconductive. This causes the emitters of the transistors 174 to behigh, which, in turn, causes the transistors 176 to be conductive. Thus,all of the leads 80-92 to the relay driver 70 are clamped to ground andnone of the llll sections ldllA-G of the relay driver can be fired. Allof the sections l'rllA-G are now in a state.

If now a first negative-going clock pulse is received on the lead 75, itwill drive the base of the transistor 3172A negatively, thus causingthat transistor to become nonconductive and its collector potential torise. This rise in collector potential is transmitted through theresistor lhdA and the capacitor 1196M. to the base of the transistor174A. That causes that transistor to become conductive and its collectorpotential to go low. This has two effects. First, it causes the clampingtransistor ll76A to become nonconductive, thus releasing the clamp onthe lead Ell to the relay driver section 150A. Second the drop inpotential of the collector of the transistor 1170A is transmittedthrough the capacitor 194A and the diode ltlZB to the base of thetransistor i728 in the second stage lli'ilh. Thus, the stage i708 flips,which similarly causes the stage l7tlC to flip, and so on down the lineuntil all stages assume a l state. in this condition, the current on theoutput lead 1110 from the accumulator 74l corresponds to 127 plus thecurrent through the resistor lllh corresponding to 20 kv. At the sametime, all of the leads lib-592 to the relay driver 7i]! are unclamped toenable all of the driver sections lllA-G to be fired upon the receipt ofthe next firing pulse from the multivibrator '72. it is noted that atthis time the diodes 182 are reverse biased, and the diodes 1183 areforward biased.

The next or second negative-going clock pulse received on the lead 75 istransmitted through the diode ltiBlA and through the resistor 188A andthe capacitor ldliA to the base of the transistor ll7lA. This causesthat base to go low and cuts off the transistor 174A. This causes thepotential of the collector of the transistor ll74A to rise. This rise inpotential is transmitted through the resistor 184A and the capacitorllEitSA to the base of the transistor 1172A, and causes that transistorto become conductive. Also, the rise in potential of the collector ofthe transistor 174A causes the transistor 176A to become conductive andclamps the lead till to ground potential. The rise in potential of thecollector of the transistor 1174A has no effect on the next-succeedingstage 1708, because the diode M328 is reverse biased and the diode WEBis forward biased. Thus, the positive pulse transmitted through thesteering diode to the already-positive base of the transistor 17413 hasno effeet. At this point in time, because the transistor l72A isconductive, current does not flow through the output resistor 94 so thatthe total current in the lead lid to the accumulator is reduced by oneunit and corresponds to 126 units plus the current due to flow throughthe resistor 118.

When a third clock pulse is received, the base of the transistor 172Awill be driven negatively. This causes the transistor 172A to becomenonconductive and the transistor ll'MA to become conductive. The drop inpotential of the collector of the transistor 17 5A is transmittedthrough the capacitor 1194A, the diode 11833, and the resistor W818 andthe capacitor was to the base of the transistor 1748. This causes thattransistor to become nonconductive, which in turn cuts oh thetransistors 1728, 1768. Thus, the total current from the accumulator onthe lead lllll is reduced by two units and corresponds to 125 plus thecurrent through the resistor lid.

The next-incoming clock pulse will cause the section 1170A to flip, butwill not afiect the section 1768. Thus, the total output current willcorrespond to 1% plus the current through the resistor lllh. Assuccessive input pulses are received, the counting proceeds in theconventional manner of binary counters until the count reaches zero. Atthat time, there is no current through the resistors 94406, and all ofthe leads hll92 are grounded through their respective transistorsll76A-G. As previously noted, the next-incoming clock pulse resets theaccumulator to provide output current corresponding to 1127, plus thebase or reference current through the resistor lit it will be recalledthat it was mentioned in connection with F181. 2 that the voltagesupplied to the accumulator 7 3 on the lead 114 from the power supplyllZ reflects variations in a number of factors. Among these, arealternating current line variations and changes in the current throughthe X-ray tube. These changes in the voltage supplied on the lead 114are reflected as percentage changes in the output currents supplied tothe lead lllltl through the resistors 94-106. In other words, a 10percent change in the voltage supplied on the lead 11M- will result in a10 percent change in the current in the lead lid for each of the variousKV levels. Thus, if the voltage on the lead lllld decreases, a highercount will be required in the accumulator 74 to provide the same outputcurrent on the lead lllll as before the change in voltage occurred. Thismeans that if, for example, the line voltage for the system decreases,at different combination of autotransformer secondary windingslldSlllldS6d will be selected (higher KV selection) to maintain theactual KV supplied to the X-ray tube at its predetermined desired value.Of course, the converse is also true.

lFllG. 5 shows schematically the remainder of the control circuitryshown in block form in FlG. 2. Various portions of the schematic diagramof FM}. 5 have been identified generally by the same reference numeralsas their corresponding blocks in H6. 2.

The clock pulse generator 76 is shown toward the left-hand side of FIG.5. The pulse generator 76 comprises a freerunning, collector-coupledmultivibrator, and is entirely conventional in design. Therefore, itwill be described only in general terms. it comprises twoNPN-transistors 210, 2H2, whose emitters are respectively groundedthrough forwardbiased diodes 2M, 216. The base of the transistor 2H0 isconnected through a resistor 218 and a line 2H9 to a positive DC source(not shown) of, for example, +20 volts, and the base of the transistor212 is similarly connected through a resistor 220. The collector of thetransistor 2W is connected to the +DC line 2119 through a load resistor222, and the collector of the transistor 2112 is similarly connectedthrough two seriesconnected resistors 224, 226. Regenerative action isprovided by connecting the collection of the transistor 212 to the baseof the transistor 21MB through a capacitor 228, and by connecting thecollector of the transistor 2m to the base of the transistor 212 througha capacitor 234).

The pulse generator 76 oscillates at a frequency of approximately 2kilocycles per second. Its essentially square wave output signals areprovided from a juncture between the resistors 224i, 226 through acapacitor 232 to the cathode of a diode 234 in the gate 7%. The anode ofthe diode 234i is connected to ground through a resistor 236 anddirectly to the lead 75, which provides negative-going clock pulses tothe accumulator 7 8 when the gate 73 is open. Whether the gate 7 8 isopen or closed is determined by signals provided to the cathode of thediode 234 on a lead 238 connected from a juncture point 246 to thecathode of the diode through a resistor 242. if the signal at thejuncture point 240 is low, the diode 2% will be forward biased and willpass the negative portions of the pulses provided form the pulsegenerator 76. lf, however, the signal at the juncture point 240 is high,the diode 234 will be reverse biased and no clock pulses will be passedto the accumulator 743. Signals are provided to the juncture point 24%through a resistor 2% from an output lead 246 of the accumulator llld,and/or from the output of the relay driver Mill on a lead 1M8.

Looking now at the comparator i108, it is seen that the currentcomparison leads lllll, ll27 are respectively connected to emitters of aPNP-transistor 250 and an NPN-transistor 252. That is, current is fedinto the comparator on the lead ll10 from the accumulator 7d, and istaken from the comparator on the lead 127 through the MA adjustment,variable resistor 12%, and the fluoroscopic KV control 230 or theradiographic KV control i332. The MA adjustment and the fluoroscopic andradiographic KV controls will be later discussed in detail.

The collectors of the transistors 250, 252 are connected directlytogether and similarly to the bases of an NPN- transistor 25d and aPNP-transistor 256. The base of the PNP- transistor 25@ is connected tothe HM: line 2119 through a resistor 253 connected in series with thehigh-KV-adjust potentiometer 120. The base of that transistor is alsoconnected to ground through two series-connected resistors 260, 262.Thus, it is seen that the transistor 250 is connected in a commonbaseconfiguration so that its collector current is substantially equal toits emitter current. The base of the transistor 252 is connecteddirectly to ground, so that that transistor is also connected in acommon-base configuration.

The comparator sensitivity adjustment resistor 136 is connected betweena juncture point 264 between the resistors 260, 262 and the emitter ofthe transistor 250. That juncture point is also connected directly tothe emitters of both of the transistors 254, 256. The collector of thetransistor 254 is connected to the +DC line 219 through a load resistor266, and the collector of the transistor 256 is connected to groundthrough a load resistor 268. The load resistors 266, 268 havesubstantially equal resistance values.

The collector of the transistor 254 is also connected through a resistor270 to the base of a PNP-transistor 272. The collector of the transistor256 is connected directly to the base of an NPN-transistor 274. Theemitter of the transistor 272 is connected directly to the +DC line 219,and its collector is connected to ground through a load resistor 276.The collector of the transistor 274 is connected directly to the +DCline 219 and its emitter is connected to ground through a load resistor278. The collector of the transistor 272 is also connected through aresistor 280 to the base of an NPN-transistor 282. The emitter of thetransistor 274 is connected through a resistor 284 to the base of anNlPN-transistor 286. The NEW- transistors 282, 286 comprise an AND gatethat serves as the output stage for the comparator 108.

The emitters of the transistors 282, 286 are both connected directly toground. The collector of the transistor 282 is connected to the +DC line219 through a load resistor 288. The collector of the transistor 282 isalso connected to the cathode of a diode 290, whose anode is connectedto the +DC line 219 through a resistor 292. A juncture between the diode200 and the resistor 292 is connected to the output lead 246.

The collector of the transistor 286 is connected to the +DC line 219through a load resistor 294. It is also connected to the cathode of adiode 296, whose anode is connected to the output lead 246. it isapparent that, if either of the transistors 282, 286 is conducting, thepotential on the output lead 246 will be low, that is, it will bevirtually at ground potential. However, if both of the transistors 282,286 are nonconductive, the potential on the output lead 246 will behigh, that is, it will be at virtually the potential of the +DC line219.

ln operation, if the current being pumped into the comparator from thelead 110 through the transistor 250 is equal to that current drainedfrom the comparator on the lead 127 through the transistor 252, neitherof the transistors 254, 256 is forward biased and neither is conducting.Therefore, the base of the transistor 272 will be high, the base of thetransistor 274 will be low, and neither of the transistors 272, 274 willbe conducting. This, in turn, causes the base of the transistor 282 tobe low, and the base of the transistor 206 to be low. Thus, neither ofthe transistor 282, 286 is conductive and the output lead 246 will behigh. This high signal trans mitted to the juncture point 240 and thenceto the gate 78 causes the gate 78 to close so that no clock pulses aretransmitted through the gate to the accumulator 70.

if more current is being pumped into the comparator through thetransistor 250 than is being drained from the comparator through thetransistor 252, the transistor 25 1 will be forward biased while thetransistor 256 will remain reverse biased. This causes the transistors274, 286 to remain nonconductive, but causes the transistors 272, 288 tobecome conductive. Thus the output lead 246 will be substantially atground potential due to current flow through the transistor 282.Similarly, if more current is being drained through the transistor 252than is being supplied through the transistor 250, the transistor 254will be reverse biased while the transistor 256 will be forward biased.Thus the transistors 272, 282 will be nonconductive, but the transistors274, 286 will be conductive. Again, the output lead 246 will besubstantially at ground potential. When either of the transistors 282,286 is conducting and the output lead 246 is low, the low signaltransmitted to the gate 78 will cause the gate to open and permitnegative-going clock pulses to be transmitted on the lead 75 to theaccumulator M. This can be prevented, however, by an overriding highsignal on the lead 248 from the relay driver M0.

As previously mentioned, the purpose of the sensitivity adjustmentresistor 136 is to provide a desired dead zone, so that minor variationsin the balance between input current and output current of thecomparator will not cause the comparator to become unbalanced. This isnecessary because current is being supplied from the accumulator to thecomparator in discrete steps. Thus, it would be possible to attain acondition where the accumulator could not provide exactly the correctamount of current to balance the comparator. Therefore, the dead zone isprovided so that if the input current is within one unit of equaling theoutput current the comparator would respond as though it were balanced.If the resistance of the variable resistor 136 is increased, thesensitivity of the comparator is increased. if the value of the resistor136 is made smaller, a greater current differential must be seen by thetransistors 254, 256 to indicate an unbalance. The dead zone may be madeas many current units wide as desired by adjusting the resistor 136,although a zone approximately one current unit wide is preferred.

As was previously mentioned, a high signal may be provided from therelay driver 160 on the lead 248 to override any low signal providedfrom the accumulator 108 and to maintain the gate 78 closed. This cannotoccur, however, when the exposure control or command switch 142 is open.

As is shown at the left of FIG. 5, the relay driver 140 comprises twoNPN-transistors 300, 302 and a PNP-transistor 304. The emitter of thetransistor 300 is connected directly to ground, and its collector isconnected directly to the base of the transistor 302. Thus, if thetransistor 300 is conducting, the base of the transistor 302 iseffectively grounded and no signals appearing on it can afiect the stateof that transistor. Conduction or nonconduction of the transistor 300 iscontrolled by the position of the exposure control switch 142. Apositive DC voltage of, for example, +28 volts, is provided on a line306 from a voltage source (not shown). The +DC line 306 is connected toone end of a resistor 308, whose other end is connected to the anode ofa diode 310. The cathode of the diode 310 is connected to ground throughthe switch 142. A juncture between the resistor 308 and the diode 310 isconnected to the anode of another diode 312, whose cathode is connectedto the base of the transistor 300. The base of the transistor 300 isalso connected to ground through a resistor 310. When the switch 142 isopen, the base of the transistor 300 is maintained at a positivepotential because of the voltage divider action of the resistor 308, thediode 312 and the resistor 314. Thus, when the switch 142 is open, thediode 300 is conducting heavily and effectively grounding the base ofthe transistor 302. Signals from the comparator 108 provided to thejuncture point 240 are provided to the base of the transistor 302through the lead 248 and a resistor 316. However, when the transistor300 is conducting, these signals have no effect on the state of thetransistor 302. When the switch M2 is closed, as when it is desired tomake an exposure, the base of the transistor 300 is effectivelygrounded, which stops conduction in that transistor. Thus, the ground isremoved from the base of the transistor 302 and it is free to vary inpotential in response to any signals received from the comparator on thelead 268.

The transistors 302, 304 act together to energize the relay coil 36C,when the base of the transistor 302 is not grounded through thetransistor 300 and a high signal is received from the comparator 108through the lead 248. The collector of the transistor 302 is connectedto the +DC line 306 through a load resistor 318 and to the base of thetransistor 304 through a resistor 320. The emitter of the transistor 302is connected to the +DC line 3% through. a resistor 322 and to groundthrough a Zener diode 324. The emitter of the transistor 3% is connectedto +DC line 3% through a Zener diode 326. Its collector is connected toground through the relay-actuating coil 36C across which a diode 32% isconnected to short circuit any transients induced in the coil 36C whencurrent through the coil is abruptly stopped. The collector of thetransistor 30% is also connected to the anode of a diode 33th. Thecathode of the diode 330 is connected through a resistor 332 to the lead248, whereby, when the transistor 3% conducts, a high signal is placedon the lead 248 to reverse bias the diode 23 in the gate 78.

When the exposure control switch M2 is closed and the base of thetransistor 302 ungrounded, a high signal present at the juncture point240 indicating balance in the comparator W3 is transferred to the baseof the transistor 3&2. This turns on the transistor 302, which decreasesits collector potential and turns on the transistor 3%. When thetransistor 3% conducts, the relay-actuating coil 36C is energized and,simultaneously, a high signal is transferred through the diode 3th andthe resistor 332 to the juncture point 24M) and thence by way of thelead 238 to the gate 78. The high signal transferred through the diode330 and the resistor 332 also maintains the base of the transistor 302at a positive potential, so that any low signals received from thecomparator W8, which might occur if the system input voltage changedduring a exposure, will not affect the conditions of the transistors3tl2, 3134. The only way that the high signal on the lead 243 from therelay driver 140 can be removed is by opening the switch 142 at thetermination of an exposure. In addition, the high signal present on lead243 from the relay driver maintains the gate 73 in an open condition sothat variations in the state of the comparator I08 during an exposurehave no effect on the gate 78. In other words, the gate 78 remains openduring an exposure to maintain the combination of autotransformersecondary windings 11481-141864 selected at the beginning of theexposure.

The exposure switch M2 is shown diagrammatically as a simple manuallyoperated switch. It will be realized, however, that in actual practicethe exposure control switch M2 would in all probability be an electronicswitch such as a phototimer or other known device that would control theX-ray exposure accurately.

As was previously mentioned in connection with the description of thecomparator 108, the comparator compares the current through thetransistor 250 with the current through the transistor 252. As describedwith reference to FIG. 4, the level of current in the conductor 110 fromthe accumulator 7d depends on the current through the resistors 941-1015and the resistor I18, and the voltage supplied to the accumulator on thelead 114 from the power supply line 1112. In turn, the voltage suppliedfrom the power supply M2 depends on the line voltage supplied to thepower supply and on the voltages added to that voltage from thehighdtV-adjust potentiometer 120, the line voltage compensationpotentiometer I22 and the MA adjustment I24.

The power supply 1112 is shown in the lower right-hand portion of FIG.5. It comprises a conventional full-wave rectifier bridge, showngenerally by the reference numeral 340, having a pair of input terminalsand a pair of output terminals. The input terminals are connected to theterminals 13A, 18B of the secondary winding MSA of the autotransforrnerlid shown in FIG. ll. Thus, the input voltage to the bridge rectifier340 will vary with the line voltage supplied to the autotransformer M.The positive output terminal of the bridge rectifier 340 is connected toground through a choke 342 and a capacitor 344 connected in series tofilter the output of the bridge. The lead 11114 to the accumulator 74!is connected to the juncture of the choke 362 and the capacitor 344.

The negative output terminal of the bridge rectifier 3410 is connectedby way of the lead 126 to the impedance-matching device I25. Theimpedance-matching device comprises two NPN-resistors 3%, 348. Thecollector of the transistor 3 is connected to the HM: line 306 through aresistor 350. The emitter of the transistor 346 is connected directly tothe base of the transistor 3% and through a resistor 352 to ground. Thecollector of the transistor 348 is connected to the +DC line 3% througha resistor 35d, and its emitter is connected directly to the lead 126 tothe power supply I112. The potential on the base of the transistor 3%determines the degree of conductivity of the transistor 3%, and hencethe level of voltage added to that provided by the power supply 112 tothe accumulator 741 on the lead M41.

The base of the transistor 3% in the impedance-matching device isconnected to one end of the line voltage compensation potentiometer 122.The other end of the potentiometer 122 is connected to the movable armof the high-KV- adjust potentiometer 12th. The adjustable arm of thecompensating potentiometer 1122 is connected to the collector of anNPN-transistor 356. The base of the transistor 356 is grounded, and theemitter of that transistor is connected through the MA adjustment 1124to a regulated source of negative direct current (not shown). The MAadjustment 124 is shown diagrammatically as a simple variable resistor,although it is pointed out that in practice it could well comprise aplurality of resistors of different values that are connected into thecircuit one at a time as various currents through the X-ray tube areprogrammed. its function is to provide a current drain through thetransistor 356 that varies inversely with the X-ray tube currentselected. In other words, if 0 milliamps are programmed into theequipment, the variable resistor 124 would represent an infiniteresistance. Similarly, as the milliamperage programmed for the X-raytube increases, the resistance value of the variable resistor 124idecreases. This causes more current to flow through the transistor 356,which reduces the voltage applied to the base of the transistor 346.When the voltage applied to the base of the transistor 346 is reduced,condition through that transistor decreases, thus reducing the voltagedrop across the resistor 352 and decreasing the potential on the base ofthe transistor 348. This, in turn, decreases conduction of thetransistor 348 and results in less voltage being added by theimpedance-matching device 125 to that supplied by the power supply 112.

As previously pointed out in connection with FIG. 2, the maximum voltagethat is added to the voltage from the power supply H2 is determined bythe adjustment of the movable arm of the high-KV-adjust potentiometer1120. The potentiometer 124) would be initially adjusted with thevariable resistor I24 set to provide infinite resistance to obtain themaximum lKV desired to be applied to the X-ray tube with all of thetransformer secondary windings 1451-14864 connected in series in thehigh-voltage transformer and rectifier input circuit. That adjustmentwould then remain constant for any particular equipment whose componentsare not changed.

As previously described with reference to FIG. 2, the current outputlead 127 of the comparator 108 is connected to supply current to an MAadjustment R28 to either a fluoroscopic KV control 130 or a radiographicKV control I32. In FIG. 5, the MA adjustment 123 is shown as a simplevariable resistor connected between the emitter of the transistor 252and the regulated negative DC source previously mentioned. In fact, theMA adjustment I28 may be the same type of device as the MA adjustmentI24 and, in some instances, even a single device can serve to provideboth adjustments.

The lead 1127 from the comparator MP8 is also connected to supplycurrent to the radiographic KV control 132, shown in the upperright-hand portion of FIG. 5, and to the fluoroscopic KV control 136)shown just below the control 132. Whether the current is provided to thefluoroscopic control 130 or to the radiographic control 132 isdetermined by the mode control switch 13 i, shown in the lowerright-hand portion of FIG. 5.

The mode control switch 134 comprises a PNP-transistor 360 and threeNPN-transistor 362, 364, 366. The conditions of the transistors 362,364i, 366 are controlled by the condition of the transistor 360 which,in turn, is controlled by the condition of a switch 368. The switch 368is manually opened or closed by a radiologist in accordance with whethera fluoroscopic exposure is to be made or a radiographic exposure is tobe made. if a radiographic exposure is to be made the switch 368 isclosed, and if a fluoroscopic exposure is to be made the switch 368 isopened. It is, of course, understood that the switch 368 is shown onlyin a diagrammatic sense. in practice, the switch 368 may well be anelectronic device that is responsive to equipment primary logiccircuitry to perform the function described hereinafter.

1n the mode control switch 134, the base of the transistor 360 isconnected through a resistor 370 to the l-DC line 386, and to groundthrough a resistor 372 and the switch 368 connected in series. Theemitter of the transistor 360 is connected directly to the ADC line 219which is less positive than the line 306. The collector of thetransistor 360 is connected through two series-connected resistors 374,376 to a line 378. A negative DC potential (approximately 8 volts) isprovided on the line 378 from a voltage source (not shown). When theswitch is closed as shown, the base of the transistor 360 is lesspositive than its emitter and the transistor 360 conducts heavily. Whenthe switch 368 is open, the base of the transistor 360 is positive withrespect to its emitter, and the transistor is nonconductive. Thus, thetransistor 360 is conductive during a radiographic mode of exposure, andis not conductive during a fluoroscopic mode of exposure.

As previously mentioned, the condition of the transistor 360 controlsthe conditions of the transistors 362, 364, 366. The transistor 362switches the radiographic KV control 132 into and out of the circuit.The transistor 366 controls the condition of another PNP-transistor 380,which switches the fluoroscopic KV control 130 into and out of thecircuit. if the transistor 362 is conducting, the radiographic KVcontrol is in the circuit, and if the transistor 366 is conducting thefluoroscopic KV control 130 is in the circuit. Obviously, thetransistors 362, 366 cannot both be in the same state at the same time.

The current lead 127 from the comparator 108 is connected to the anodeof a diode 382, which serves as an input element for the fluoroscopic KVcontrol 130. The lead 127 is also connected to the anode of anotherdiode 384, which serves as an input element for the radiographic KVcontrol 132.

in the fluoroscopic KV control 130, the collector of the transistor 380is connected directly to the DC line 378. The emitter of that transistoris connected through a resistor 386 to the cathode of the input diode382. The base of the transistor 380 is connected to the movable arm of apotentiometer 388 that serves as the fluoroscopic KV adjustment. One endof the potentiometer 388 is connected through a variable resistor 390 toground, and the other end of the potentiometer is connected directly tothe collector of the transistor 366. The emitter of the transistor 366is connected directly to the DC line 378. Therefore, if the transistor366 is nonconductive, the base of the transistor 380 will be essentiallyat ground potential, and the transistor 380 will be nonconductive.Therefore, the fluoroscopic KV control channel will be closed. If thetransistor 366 is conductive, the base of the transistor 380 will be ata negative potential determined by the setting of the movable arm of thepotentiometer 388. Thus, current flow through the transistor 380 will bedetermined by the setting of the movable arm of the potentiometer 388.The variable resistor 390 serves as a calibration adjustment for thefluoroscopic KV control.

The radiographic KV control 132 comprises a plurality of normally openswitches 392A-H and a plurality of fixed resistors 394A-H. Correspondingones of the switches 392A-G and the resistors 394A-G are connected inseries between input and output leads 396, 398. The lead 396 isconnected to the cathode of the input diode 384, and the lead 398 isconnected directly to the collector of the transistor 362 and to groundthrough a resistor 400. The emitter of the transistor 362 is connecteddirectly to the DC line 378. Therefore, if the transistor 362 isconductive, those resistors 394 whose corresponding switches 392 areclosed are connected in parallel between the lead 127 and the DC line378. The purpose of the input diode 384 is to insure that, when thetransistor 362 is nonconductive and one or more of the switches 392 isclosed, current cannot flow back through the resistor 400 and into thelead 127.

The resistors 394A-G are chosen to permit various numbers of units ofcurrent to flow through them, when their corresponding switches 392A-Gare closed. For example, the resistor 394A could have a relatively largevalue, so as to permit one unit of current to flow through it, when itscorresponding switch 392A is closed. The resistor 3941) could have avalue half that of the resistor 394A to permit two units of current toflow through it when the switch 3928 is closed. The values of theresistors 394(1-6 would become progressively smaller to permitincreasing numbers of units of current to flow through them when theircorresponding switches are closed. It is pointed out that eight switches392 are resistors 394 are shown in a diagrammatic sense only. inpractice, there might well be 23 such combinations. In such anarrangement, the 23 resistors might well be sized to permit current flowof l, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30,40, 50, 60, 70, 80, 90, 100,I10, 120, and units. These units of current, of course, would correspondto selected KV levels of 1 kv., 2 kv., Alternatively, eight combinationsof switches and resistors might be used, with the resistors so sizedthat current through them would correspond to voltages applied to theX-ray tube of l 2 kv., 4 kv., 8 16 32 kv., 64 kv., and 128 kv. The firstexample given is probably preferably, however, because only two switchesneed be closed to obtain any desired KV value. in the second example,various combinations of switches would have to be closed and could beconfusing to an operator.

Attention is drawn to the fact that the control system will not respondto permit an exposure to be made if any of the switches 392'are closedthat represent a total selected KV of less than that represented bycurrent through the low-KV-adjust resistor 118 shown in FIG. 4. in otherwords, if the total KV selected by closing the switches 392 in acombination that calls for less than that predetermined by the settingof the resistor 118, more current will be pumped into the comparator 108on the lead 110 from the accumulator 74 than will be drained from thecomparator on the lead 127 through the radiographic KV control 132. Inthat instance, the accumulator 168 will never balance to provide a highoutput signal, so that the relay driver 140 will never be energized andno X-ray exposure can be made.

Turning again to the mode control switch 134, it is seen that the baseof the transistor 362 that opens and closes the radiographic KV controlchannel is connected to a point intermediate between the resistors 374,376 in the collector circuit of the transistor 360. The base of thetransistor 364 is connected through a resistor 402 to the collector ofthe transistor 360, and is connected through a resistor 404 to the DCline 378. The collector of the transistor 364 is connected directly tothe base of the transistor 366 and to ground through a load resistor486. The emitter of the transistor 364 is connected directly to the DCline 378.

As previously noted, when the mode control switch 134 is in theradiographic mode of operation the switch 368 is closed. This causes thetransistor 360 to conduct and provide a voltage drop across the loadresistors 374, 376. The potential drop across the resistor 376 causesthe base of the transistor 362 to be positive with respect to itsemitter and causes that transistor to become conductive. This enablesthe radiographic l(V control channel and permits current flow throughthose resistors 394A-H whose corresponding switches 392A-H are closed.At that same time, the base of the transistor 364 is also positive withrespect to its emitter, because of the potential drop across theresistor 404. This causes the transistor 364 to become conductive. Thepotential on the collector of the transistor 364 and hence on the baseof the transistor 366 is essentially the same as the potential of the DCline 378. This causes the transistor 366 to be nonconductive anddisables the fluoroscopic KV control channel.

When the radiologist opens the switch 356% in order to malre afluoroscopic examination, the potential at the base of the transistor36% rises and that transistor cease conducting. This causes thepotential at the base of the transistor 36?; to drop and cuts off thattransistors to disable the radiographic lKV control channel. At thatsame time, the potential at the base of the transistor 364 goes negativeand that transistor cuts off. This causes its collector and the base ofthe transistor 3% to go to ground potential and causes the transistor3366 to become conductive. This enables the fluoroscopic ltV controlchannel by permitting current through the fluoroscopic liV adjustpotentiometer 3%.

Although the various portions of an embodiment of a control systemembodying the invention have been described in detail, it is believedthat a brief description of the overall operation of the system will behelpful. The following descrip tion is primarily of a functional nature,and is made principally with reference to FIGS. ll 2 and 5. Onlyincidental reference will be made to the detailed circuitry shown inW63. 3 and t.

The equipment is initially energized by closing the input power switch16. This provides primary power to the autotransformer M and energizesthe various power supplies that are connected to the transformersecondary windings MSA, MSB, MSC. When the various power supplies areenergized, several things occur. For example, the second multivibrator1144 is energized to provide an inhibit signal on the lead 69 to the SCRswitch 58 so that that switch is maintained open and no voltage can beapplied through the leads 52, 54 to the high-voltage transformer andrectifier circuit 565. The clock pulse generator 76 is energized toprovide clock pulses to the gate 7% and thence to the accumulator 74 ifthe gate 7% is open. The relay driver 70 is energized, and voltage isapplied to the accumulator 74 on the lead 1M from the power supply 1112.Likewise, the comparator 11% is energized to provide output signals onthe lead l38 to the gate 78 and to the relay driver 141). At this time,the exposure control switch 1l4l2 is open, so that the relay driver M isinoperative.

Assume now that the switch 36% in the mode control switch 134 ((FlG. hasbeen left open from a previous exposure. In that case, a certain amountof current will be drained from the comparator 1% through the lead 127and through the transistor 380 in the fluoroscopic KV control 130. Anadditional current drain will occur through the MA adjustment 12%depending on what its previous setting was. Assume also that the high KVadjustment potentiometer B20, the line voltage compensationpotentiometer ll22, and the MA adjustment 12d are providing a certainvoltage that is added to the voltage provided by the power supply 112 onthe lead lid to the accumulator. Assume further that when the equipmentwas last deenergized the accumulator 74 was provided a certain level ofcurrent through the resistors 94-11% to the lead llltt connected to thecurrent input of the comparator lldd. if that current is not the same asthe current being drained from the current output on the lead ll27 fromthe comparator, the com parator will provide a low output signal on thelead 113% to the gate 78 to open the gate. The clock pulses transmittedfrom the clock pulse generator 76 through the gate 78 to the accumulator74 will then cause the accumulator to start counting as previouslydescribed and vary the current supplied to the lead ill) in steps of onecurrent unit to the comparator. When the current input to the comparatoron the lead lllli'i equals the current output on the lead 1127, thecomparator will provide a high output signal on the lead 138 which willcause the gate 78 to close. This signal will have no effect on the relaydriver because the exposure control switch 142 is still open.

Because the relay driver 114% is not actuated, the relay coil 36C is notenergized and the first multivibrator 72 is not actuated. Therefore,although various ones of the leads hill-92 from the accumulator to therelay driver 70 are being energized, it will have no effect on the relaydriver 7d because no firing pulse will be received from the firstmultivibrator 72. Thus, there will be no output on the leads M l-5h fromthe relay driver to the relays 20-332 to provide energizing current totheir actuating coils EGG-32C. Furthermore, the relay con- Zli tacts 36Awill be open, so that the relay coils 2tiC-32C would not be energizedeven though the leads 33-50 were energized.

The same functions would occur were the switch 368 in the mode controlswitch 134 in a closed position. The only difference would be that thecomparator ltltl would provide a high output signal on the lead 138 whenthe current drain through the lead 1127 (controlled by the condition ofthe switches 392 in the radiographic KV control 132) was equal to thecurrent input from the accumulator on the lead 110.

The radiologist would then adjust the various controls for the exposurethat he desired to make. if the exposure was to be of the radiographictype, the switch 368 in the mode con trol switch 1134 would be closed.This would open the radiographic KV control channel through thetransistor 362 and close the fluoroscopic KV control channel through theresistor 366. One or more of the switches 392 in the radiographic KVcontrol 132 would then be closed to correspond to the desired KV levelto be applied to the X-ray tube. The desired current through the X-raytube would then be selected and the MA adjustments 1%, 12% madeaccordingly, high resistance values for low tube current and lowresistance values for higher tube currents. Thus, a certain voltagewould be subtracted from the voltage provided the accumulator on thelead llld from the power supply M2 in accordance with the selected MAvalue, and a certain current drain would be provided through the MAadjustment 128 to provide for losses in the system that are proportionalto X-ray tube current. As these adjustments are made, the current outputfrom the comparator MM on the lead ll27 is changed. The comparator thusprovides a low output signal on the lead 138 to open the gate 73 andpermit clock pulses to be provided to the accumulator 74. Theaccumulator 74! then counts until the currents supplied through itsoutput resistors 94-196 (and the current provided trough the low ltVadjustment resistor 118) on the lead llltb equal the current drainedfrom the comparator on the lead 127. When those two currents are equal,the comparator again provides a high output signal on the lead 138 whichcloses the gate 78 and maintains the accumulator 74 at its last countcondition.

If, during that period of time between initial energization of theequipment and closing of the exposure command switch M2, the input linevoltage to the system changes that change will be reflected in thevoltage supplied to the power supply M2 and in the voltage supplied fromthe power supply to the accumulator 74 on the lead M. As previouslynoted, if the input voltage decreases, the voltage supplied to theaccumulator will decrease and a higher count will be required from theaccumulator to provide a current on the lead 1110 to the comparator 108that equals the current on the lead 127 drained from the accumulatorthrough the RV controls 130, 132 and the MA adjustment 12%. Of course,the converse is true. If the input voltage increases, a lower count willbe required from the accumulator to cause the comparator to balance.

After the KV adjustments and the MA adjustment and the mode controlselection has been made, the exposure command switch M2 may be closed.At that time, if the current to the comparator ltitl on the lead llllhis equal to the current from the comparator on the lead 127, a highoutput signal will be provided on the lead 138 to the relay driver 140and to the gate 78. This will cause the gate 78 to close and maintainthe accumulator at that particular count. As previously described,closing the switch M2 releases the clamp on the input to the relaydriver M0 and the high signal provided on the lead 138 will actuate therelay driver. This will simultaneously cause the relay-actuating coil3M: to be energized and a high signal provided on the lead l lll to thegate 78 to maintain the gate in its last-attained condition regardlessof any further changes in the output from the comparator W8. Thus, anychanges in the input line voltage during the course of an exposurecannot cause the various relays 2042 to change their conditions. Inother words, those autotransformer secondary windings lest-M364 that areconnected in series at the beginning of an exposure remain so connectedthroughout the exposure.

This is necessary because the contacts of the relays 2 11-32 cannot beopen and closed while current is flowing through them because of theirphysical or structural limitations.

When the relay actuating coil is energized, it closes the normally openrelay contacts 36A, 3613. The contacts 36A, when closed, complete acurrent path from the relay-actuating coils 20C-32C to ground, so thatthose relays whose leads 38-561 from the relay driver 70 are energizedcan be actuated. When the relay contacts 3613 close, the firstmultivibrator 72 is actuated to provide a positive firing pulse on thelead 73 to the relay driver 70, after a very short time delay.

At the time the positive firing pulseis received on the lead 73 by therelay driver 70 from the first multivibrator 72, selected ones of theleads h-92 have signals thereon. Those SCRs 152A-G that are receivinghigh signals on the leads 80-92 are fired by the firing pulse from themultivibrator to energize corresponding ones of the output leads 3840.This energizes corresponding ones of the relays 20-32 and connectscorresponding ones of the autotransformer secondary windings 1481-14864in series with the reference voltage winding 145R to the input of thehigh-voltage transformer and rectifier circuit 56.

The second multivibrator 144 receives a signal from the firstmultivibrator 72 simultaneously with the firing pulse provided on thelead 73 to the relay driver 70. After a relatively short time delay, themultivibrator 144 removes the inhibit signal provided on the lead 60 tothe SCR switch 58 to permit voltage to be supplied to the high-voltagetransformer and rectifier circuit 56 and an exposure to be made. Theexposure is terminated by opening the exposure command switch 142 which,as previously pointed out, would in practice probably be an electroniccontrol which would function as a switch to provide exposures ofvariable desired durations.

At the end of an exposure, when the switch 142 is opened, the controlsystem assumes essentially the same condition as initially described.The relay driver 140 becomes inoperative, and the gate 78 will close orremain closed when the input current on the lead 1 to the comparator 108is equal to the output current on the lead 127. The various controls maythen be adjusted for the next exposure.

if a fluoroscopic mode of exposure is desired, the switch 368 in themode control switch 134 is opened, this causes current in the lead 127from the comparator to be provided to the fluoroscopic control 130 andto the MA adjustment 128 rather than to the radiographic KV control 132and the MA adjustment 128. Outside of the different current path fromthe lead 127, the operation of the system is exactly the same as thatdescribed with respect to the radiographic mode of operation.

Although one embodiment of the invention has been illustrated anddescribed in detail, it is apparent that many modifications andvariations can be made by one skilled in the art departing from the truespirit and scope of the invention.

llclaim:

1. An X-ray control system for selecting energizing voltages to besupplied to an X-ray tube comprising:

a. a transformer having a primary winding for connection to a source ofvoltage, and having a plurality of secondary windings for providing saidenergizing voltage to said X- ray tube, said secondary windingsrespectively providing different voltage outputs;

b. voltage selection means for connecting selected ones of saidsecondary winding to the X-ray tube to provide different selectedenergizing voltages thereto;

0. X-ray tube energization control means interposed between the X-raytube and the secondary windings for selectively connecting the X-raytube across the secondary windings; and

d. inhibit control means connected to the X-ray tube energizationcontrol means and to the voltage selection means, said inhibit controlmeans permitting the Xray tube energizafion control means to connect theX-ray tube to the secondary windings only after the secondary windingshave been connected in the combination required to provide the voltageselected by the voltage selection means.

2. An X-ray control system for selecting energizing voltages to besupplied to an X-ray tube comprising:

a. a transformer having a primary winding for connection to a source ofvoltage, and having a plurality of secondary windings for providing saidenergizing voltage to said X- ray tube, said secondary windingsrespectively providing different voltage outputs; and

b. voltage selection means for connecting selected ones of saidsecondary windings to the X-ray tube to provide different selectedenergizing voltages thereto, and comprismg i. a plurality of switchingdevices;

ii. a ltilovoltage selector having a plurality of kilovoltage settings;

iii. control circuit means for causing said switching devices to connectthe secondary windings progressively in different combinations to scanthe kilovoltage range selectable from the transformer; and

iv. comparison means for comparing the kilovoltage level selected onsaid kilovoltage selector to the voltage output of the secondarywindings connected together, and providing a signal indication when thevoltage output of the connected windings is the voltage selected.

3. The system of claim 2 wherein the secondary windings are sized andarranged so that their respective voltage outputs are proportional toelements in a geometric series.

d. The system of claim 3 wherein the geometric series is binary.

5. The system of claim 4 wherein the binary-coded windings are sized andconnected to scan in equivalent voltage steps corresponding toapproximately 1.0 kv. each as provided to the X-ray tube.

6. The system of claim 5, wherein seven binary-coded secondary windingsare provided and have output voltage values equivalent to l, 2, 4, 8,16, 32 and 64 kv. as supplied to the X-ray tube.

7. An X-ray control system for selecting energizing voltages to besupplied to an X-ray tube comprising:

a, a transformer having a primary winding for connection to a source ofline voltage, and having a plurality of secondary windings for providingsaid energizing voltage to said X-ray tube, said secondary windingsrespectively providing different voltage outputs; and

b. voltage selection means for connecting selected ones of saidsecondary windings to the X-ray tube to provide different selectedenergizing voltages thereto and comprismg i. a plurality of switchingdevices for selectively connecting the secondary windings in differentseries combinations to provide different selected X-ray tube energizingvoltages.

kilovoltage selector means settable to any one of a plurality ofkilovoltage settings of an available kilovoltage range and having anoutput providing a first signal indication which varies according to thekilovoltage settings,

iii. binary-coded winding selection means connected to said switchingdevices and causing said switching devices to connect said binary-codedwindings progressively in a plurality of combinations which will providethe kilovoltage range selectable on said kilovoltage selector,

iv. said binary-coded winding selection means having an output providinga second signal indication which varies according to the voltageprovided to the connected binary-coded windings,

v. comparison means comparing the first and second signal indicationsfrom the outputs of the kilovoltage selector means and the binarycodedwinding selection means and providing a control signal when the signalindications are equal, and

vi. energizing circuit control means for initiating energization of theX-ray tube in response to said control signal.

8. The system of claim 7, wherein said voltage selection means furthercomprises:

vi. loss compensator means connected to said kilovoltage selector meansto modify the first signal indication provided by said kilovoltageselector means in accordance with direct current losses so that anothercombination of the binary-coded secondary windings must be selected tocause the first and second signal indications to be equal.

9. The system of claim 8, wherein the signal indication from one of saidoutputs is dependent upon said source of line voltage so that changes insupplied line voltage cause corresponding changes in the selectedcombination of binary-coded secondary windings necessary to maintain apreselected KV to be supplied to the X-ray tube.

10. The system of claim 7, wherein said kilovoltage selector meanscomprises a plurality of kilovoltage selectors selectively connectableto said comparison means for selecting one of a plurality ofkilovoltages to be supplied to the X-ray tube.

11. An X-ray system comprising:

a. a transformer having a primary winding and a plurality ofbinary-coded secondary winding, each succeeding secondary windingproviding twice the output voltage of a preceding winding;

b. a like plurality of switching devices for connecting selectedbinary-coded winding in series;

c. circuit means for connecting the series-connected windings to theinput of the high-voltage transformer and for connecting an output ofthe high-voltage transformer to an X-ray tube;

d. kilovoltage selection means for selecting a kilovoltage to besupplied to the X-ray tube; and

e. winding selection control means including i. sequencing means forsequentially selecting ditferent combinations of binary-coded windings;

ii. signal means for indicating the binary-coded windings selected;

iii. comparison means connected to said signal means and to saidkilovoltages selecting means for comparing the kilovotlage providable bythe binary-coded windings selected to the selected kilovoltage andproviding a control signal when the voltage providabie by the selectedbinary-coded windings equals the selected voltage; and

iv. energization control means connected to said switching devices andto said comparison means and energizing selected switching devices forconnecting the selected binary-coded windings in series in response tosaid control signal.

112. The system of claim lli, wherein said sequencing means comprises abinary counter, said counter having a plurality of first outputs equalto said plurality of secondary windings and switching devices whichfirst outputs are energized to provide binary indications of the totalpulse count received by the counter at its input for a pulse generator,said first outputs being connected to said switching devices so thatonly those switching devices connected to an energized first output canbe energized by said energization control means.

13. The system of claim 12, wherein said signal means is a current addercomprising a plurality of resistors having respective one ends connectedto respective second outputs of said binary counter and their other endsconnected to a common conductor, the resistance of each succeedingresistor is one-half that of its next preceding resistor and theresistors are energized through the second outputs of the binary counterfrom a common voltage supply, whereby the current in the commonconductor is representative of the voltage providable by thebinary-coded windings selected.

M. The system of claim li, wherein said sequencing means comprises:

i. a binary counter;

ii. a clock pulse generator providing bits to a input of said counter;

iii. a gate interposed between said counter and said pulse generator forcontrolling passage of said bits to said input of said counter;

iv. said counter having a plurality of outputs equal to said pluralityof switching devices which are selectively energized to provide a binaryindication of total bit count received by said counter, said outputsbeing respectively connected to said switching devices so that onlythose switching devices connected to an energized output can beenergized by said energization control means; and I v. said gate beingconnected to said comparison means and stopping passage of said bits tosaid counter in response to said control signal.

15. In an X-ray control system for selecting energizing voltages to besupplied to an X-ray tube, the combination comprising:

a. a transformer having a primary winding for connection to a source ofline voltage, and having a plurality of secondary windings for providingsaid energizing voltages to said X-ray tube, said secondary windingsrespectively providing different voltages outputs;

b. a clock pulse generator for providing clock pulses;

c. selecting means responsive to said clock pulses for sequentially andcyclically connecting various ones of said secondary windings to providevarious energizing voltages for said X-ray tube, and to provide a firstcurrent signal that varies in accordance with said voltages provided tosaid X-ray tube;

d. kilovoltage selector means for said X-ray tube, having a plurality ofkilovoltage settings to provide a second current signal that varies inaccordance with a kilovoltage selected thereby;

e. current comparator means connected to receive and compare said firstand second current signals and provide a control signal when said firstand second current are equal;

f. gate means interposed between said pulse generator and said selectingmeans responsive to said control signal to prevent transmission of saidclock pulses to said selecting means; and

g. switch means actuatable for connecting, to energize said X-ray tube,that combination of secondary windings existing when said transmissionof clock pulses is interrupted by said gate means.

116. The combination of claim 15, wherein said selecting means includesa counter.

17. The combination of claim 16, wherein said counter is a binarycounter.

18. The combination of claim 15 wherein said selecting means includes acounter having a plurality of output leads corresponding to saidplurality of secondary windings which, when selectively energized,permit various ones of said secondary windings to be connected togetherto provide said various voltages for said X-ray tube.

19. The combination of claim 18, wherein said selecting means furtherincludes driver means connected between said counter output leads andsaid secondary windings and said driver means is responsive to a firingsignal to actuate said switch means to connect in series those secondarywindings that correspond to energized output leads from said counter.

20. The combination of claim 19, further including means for providingsaid firing signal in delayed response to said control signal.

211. The combination of claim 15, further including h. milliampereselector means having a plurality of settings,

each setting corresponding to a desired current through said X-ray tubeand providing a third current signal that varies in accordance with amilliarnperage selected thereby; and

i. circuit means connecting said milliamperage selector means to saidkilovoltage selector means whereby said third current signal modifiessaid second current signal.

22. The combination of claim 15, further including h. milliamperageselector means having a plurality .of settings, each settingcorresponding to a desired current through said X-ray tube and providinga voltage signal that varies inversely with a milliamperage selectedthereby; and

i. circuit means connecting said milliamperage selector means to saidselecting means, whereby said voltage signal modifies said first currentsignal.

23. The combination of claim 15, further including h. first milliampereselector means having a plurality of settings, each settingcorresponding to a desired current through said X-ray tube and providinga third current signal that varies in accordance with a milliamperageselected thereby;

. first circuit means connecting said first milliamperage selector meansto said kilovoleage selector means, whereby said third current signalmodifies said second current signal;

j. second millamperage selector means having a plurality of settings,each setting corresponding to a desired current through said X-ray tubeand providing a voltage signal that varies inversely with amilliamperage selected thereby; and

k. second circuit means connecting said second milliamyerage selectormeans to said selecting means, whereby the voltage signal modifies saidfirst current signal.

24. The combination of claim 15, further including h. X-ray tubeenergization control means interposed between said secondary windingsand said X-ray tube and selectively actuatable to connect said X-raytube across said secondary windings.

25. The combination of claim 24, further including i. means foractuating said energization control means in response to said controlsignal from said comparator means.

26. The combination of claim 25, wherein said energization control meansis actuated after said switch means is actuated.

27. The combination of claim 15, further including means for energizingsaid selecting means from said source of line voltage, whereby saidfirst current signal varies in accordance with said line voltage.

28. The combination of claim 21, further including means for energizingsaid selecting means from said source of line voltage, whereby saidfirst current signal varies in accordance with said line voltage.

29. The combination of claim 22, further including means for energizingsaid selecting means from said source of line voltage, whereby saidfirst current signal varies in accordance with said line voltage.

30. The combination of claim 23, further including means for energizingsaid selecting means from said source of line voltage, whereby saidfirst current signal varies in accordance with said line voltage.

1. An X-ray control system for selecting energizing voltages to besupplied to an X-ray tube comprising: a. a transformer having a primarywinding for connection to a source of voltage, and having a plurality ofsecondary windings for providing said energizing voltage to said X-raytube, said secondary windings respectively providing different voltageoutputs; b. voltage selection means for connecting selected ones of saidsecondary winding to the X-ray tube to provide different selectedenergizing voltages thereto; c. X-ray tube energization control meansinterposed between the X-ray tube and the secondary windings forselectively connecting the X-ray tube across the secondary windings; andd. inhibit control means connected to the X-ray tube energizationcontrol means and to the voltage selEction means, said inhibit controlmeans permitting the X-ray tube energization control means to connectthe X-ray tube to the secondary windings only after the secondarywindings have been connected in the combination required to provide thevoltage selected by the voltage selection means.
 2. An X-ray controlsystem for selecting energizing voltages to be supplied to an X-ray tubecomprising: a. a transformer having a primary winding for connection toa source of voltage, and having a plurality of secondary windings forproviding said energizing voltage to said X-ray tube, said secondarywindings respectively providing different voltage outputs; and b.voltage selection means for connecting selected ones of said secondarywindings to the X-ray tube to provide different selected energizingvoltages thereto, and comprising i. a plurality of switching devices;ii. a kilovoltage selector having a plurality of kilovoltage settings;iii. control circuit means for causing said switching devices to connectthe secondary windings progressively in different combinations to scanthe kilovoltage range selectable from the transformer; and iv.comparison means for comparing the kilovoltage level selected on saidkilovoltage selector to the voltage output of the secondary windingsconnected together, and providing a signal indication when the voltageoutput of the connected windings is the voltage selected.
 3. The systemof claim 2, wherein the secondary windings are sized and arranged sothat their respective voltage outputs are proportional to elements in ageometric series.
 4. The system of claim 3, wherein the geometric seriesis binary.
 5. The system of claim 4 wherein the binary-coded windingsare sized and connected to scan in equivalent voltage stepscorresponding to approximately 1.0 kv. each as provided to the X-raytube.
 6. The system of claim 5, wherein seven binary-coded secondarywindings are provided and have output voltage values equivalent to 1, 2,4, 8, 16, 32 and 64 kv. as supplied to the X-ray tube.
 7. An X-raycontrol system for selecting energizing voltages to be supplied to anX-ray tube comprising: a. a transformer having a primary winding forconnection to a source of line voltage, and having a plurality ofsecondary windings for providing said energizing voltage to said X-raytube, said secondary windings respectively providing different voltageoutputs; and b. voltage selection means for connecting selected ones ofsaid secondary windings to the X-ray tube to provide different selectedenergizing voltages thereto and comprising i. a plurality of switchingdevices for selectively connecting the secondary windings in differentseries combinations to provide different selected X-ray tube energizingvoltages, ii. kilovoltage selector means settable to any one of aplurality of kilovoltage settings of an available kilovoltage range andhaving an output providing a first signal indication which variesaccording to the kilovoltage settings, iii. binary-coded windingselection means connected to said switching devices and causing saidswitching devices to connect said binary-coded windings progressively ina plurality of combinations which will provide the kilovoltage rangeselectable on said kilovoltage selector, iv. said binary-coded windingselection means having an output providing a second signal indicationwhich varies according to the voltage provided to the connectedbinary-coded windings, v. comparison means comparing the first andsecond signal indications from the outputs of the kilovoltage selectormeans and the binary-coded winding selection means and providing acontrol signal when the signal indications are equal, and vi. energizingcircuit control means for initiating energization of the X-ray tube inresponse to said control signal.
 8. The system of claim 7, wherein saidvoltage selection means further comprises: Vi. loss compensator meansconnected to said kilovoltage selector means to modify the first signalindication provided by said kilovoltage selector means in accordancewith direct current losses so that another combination of thebinary-coded secondary windings must be selected to cause the first andsecond signal indications to be equal.
 9. The system of claim 8, whereinthe signal indication from one of said outputs is dependent upon saidsource of line voltage so that changes in supplied line voltage causecorresponding changes in the selected combination of binary-codedsecondary windings necessary to maintain a preselected KV to be suppliedto the X-ray tube.
 10. The system of claim 7, wherein said kilovoltageselector means comprises a plurality of kilovoltage selectorsselectively connectable to said comparison means for selecting one of aplurality of kilovoltages to be supplied to the X-ray tube.
 11. An X-raysystem comprising: a. a transformer having a primary winding and aplurality of binary-coded secondary windings, each succeeding secondarywinding providing twice the output voltage of a preceding winding; b. alike plurality of switching devices for connecting selected binary-codedwinding in series; c. circuit means for connecting the series-connectedwindings to the input of a high-voltage transformer and for connectingan output of the high-voltage transformer to an X-ray tube; d.kilovoltage selection means for selecting a kilovoltage to be suppliedto the X-ray tube; and e. winding selection control means including i.sequencing means for sequentially selecting different combinations ofbinary-coded windings; ii. signal means for indicating the binary-codedwindings selected; iii. comparison means connected to said signal meansand to said kilovoltage selection means for comparing the kilovoltageprovidable by the binary-coded windings selected to the selectedkilovoltage and providing a control signal when the voltage providableby the selected binary-coded windings equals the selected voltage; andiv. energization control means connected to said switching devices andto said comparison means and energizing selected switching devices forconnecting the selected binary-coded windings in series in response tosaid control signal.
 12. The system of claim 11, wherein said sequencingmeans comprises a binary counter, said counter having a plurality offirst outputs equal to said plurality of secondary windings andswitching devices which first outputs are energized to provide binaryindications of the total pulse count received by the counter at itsinput for a pulse generator, said first outputs being connected to saidswitching devices so that only those switching devices connected to anenergized first output can be energized by said energization controlmeans.
 13. The system of claim 12, wherein said signal means is acurrent adder comprising a plurality of resistors having respective oneends connected to respective second outputs of said binary counter andtheir other ends connected to a common conductor, the resistance of eachsucceeding resistor is one-half that of its next preceding resistor andthe resistors are energized through the second outputs of the binarycounter from a common voltage supply, whereby the current in the commonconductor is representative of the voltage providable by thebinary-coded windings selected.
 14. The system of claim 11, wherein saidsequencing means comprises: i. a binary counter; ii. a clock pulsegenerator providing bits to an input of said counter; iii. a gateinterposed between said counter and said pulse generator for controllingpassage of said bits to said input of said counter; iv. said counterhaving a plurality of outputs equal to said plurality of switchingdevices which are selectively energized to provide a binary indicationof total bit count received by said counter, said outputs beingrespectively connected To said switching devices so that only thoseswitching devices connected to an energized output can be energized bysaid energization control means; and v. said gate being connected tosaid comparison means and stopping passage of said bits to said counterin response to said control signal.
 15. In an X-ray control system forselecting energizing voltages to be supplied to an X-ray tube, thecombination comprising: a. a transformer having a primary winding forconnection to a source of line voltage, and having a plurality ofsecondary windings for providing said energizing voltages to said X-raytube, said secondary windings respectively providing different voltagesoutputs; b. a clock pulse generator for providing clock pulses; c.selecting means responsive to said clock pulses for sequentially andcyclically connecting various ones of said secondary windings to providevarious energizing voltages for said X-ray tube, and to provide a firstcurrent signal that varies in accordance with said voltages provided tosaid X-ray tube; d. kilovoltage selector means for said X-ray tubehaving a plurality of kilovoltage settings to provide a second currentsignal that varies in accordance with a kilovoltage selected thereby; e.current comparator means connected to receive and compare said first andsecond current signals and provide a control signal when said first andsecond current are equal; f. gate means interposed between said pulsegenerator and said selecting means and responsive to said control signalto prevent transmission of said clock pulses to said selecting means;and g. switch means actuatable for connecting, to energize said X-raytube, that combination of secondary windings existing when saidtransmission of clock pulses is interrupted by said gate means.
 16. Thecombination of claim 15, wherein said selecting means includes acounter.
 17. The combination of claim 16, wherein said counter is abinary counter.
 18. The combination of claim 15, wherein said selectingmeans includes a counter having a plurality of output leadscorresponding to said plurality of secondary windings which, whenselectively energized, permit various ones of said secondary windings tobe connected together to provide said various voltages for said X-raytube.
 19. The combination of claim 18, wherein said selecting meansfurther includes driver means connected between said counter outputleads and said secondary windings and said driver means is responsive toa firing signal to actuate said switch means to connect in series thosesecondary windings that correspond to energized output leads from saidcounter.
 20. The combination of claim 19, further including means forproviding said firing signal in delayed response to said control signal.21. The combination of claim 15, further including h. milliampereselector means having a plurality of settings, each settingcorresponding to a desired current through said X-ray tube and providinga third current signal that varies in accordance with a milliamperageselected thereby; and i. circuit means connecting said milliamperageselector means to said kilovoltage selector means whereby said thirdcurrent signal modifies said second current signal.
 22. The combinationof claim 15, further including h. milliamperage selector means having aplurality of settings, each setting corresponding to a desired currentthrough said X-ray tube and providing a voltage signal that variesinversely with a milliamperage selected thereby; and i. circuit meansconnecting said milliamperage selector means to said selecting means,whereby said voltage signal modifies said first current signal.
 23. Thecombination of claim 15, further including h. first milliampere selectormeans having a plurality of settings, each setting corresponding to adesired current through said X-ray tube and providing a third currentsignal that varies in accordance with a milliampErage selected thereby;i. first circuit means connecting said first milliamperage selectormeans to said kilovoltage selector means, whereby said third currentsignal modifies said second current signal; j. second milliamperageselector means having a plurality of settings, each settingcorresponding to a desired current through said X-ray tube and providinga voltage signal that varies inversely with a milliamperage selectedthereby; and k. second circuit means connecting said secondmilliamperage selector means to said selecting means, whereby thevoltage signal modifies said first current signal.
 24. The combinationof claim 15, further including h. X-ray tube energization control meansinterposed between said secondary windings and said X-ray tube andselectively actuatable to connect said X-ray tube across said secondarywindings.
 25. The combination of claim 24, further including i. meansfor actuating said energization control means in response to saidcontrol signal from said comparator means.
 26. The combination of claim25, wherein said energization control means is actuated after saidswitch means is actuated.
 27. The combination of claim 15, furtherincluding means for energizing said selecting means from said source ofline voltage, whereby said first current signal varies in accordancewith said line voltage.
 28. The combination of claim 21, furtherincluding means for energizing said selecting means from said source ofline voltage, whereby said first current signal varies in accordancewith said line voltage.
 29. The combination of claim 22, furtherincluding means for energizing said selecting means from said source ofline voltage, whereby said first current signal varies in accordancewith said line voltage.
 30. The combination of claim 23, furtherincluding means for energizing said selecting means from said source ofline voltage, whereby said first current signal varies in accordancewith said line voltage.